Transient voltage suppressor devices are essentially diodes designed to be incorporated into an electrical circuit to protect that circuit against excessive voltage by breaking down and conducting if the voltage applied to them exceeds a predetermined value. Such devices usually constitute two such diodes electrically connected in opposing relation so as to protect against excessive voltage in either direction. The breakdown voltage at which such devices function depends to a large extent on the impurity concentration and depth of diffusion into the substrate. Hence variations in those parameters and particularly depth of diffusion at different points across the surface of the substrate are most undesirable. For that reason it has in the past been thought to be essential, if an effective yield of properly acting devices is to be obtained, that the substrate surfaces must be highly polished, and anything short of that high polish was thought to be commercially excluded. Polishing is an extremely time-consuming process, and when it is considered that bi-directional transient voltage suppressors of the prior art require that both opposing surfaces of the substrate be polished, the economic problems presented by the need for polishing are doubled.
Industry standard steps for obtaining a prior art mirror-like polished surface on a substrate include saw slicing, mechanical lapping, cleaning, edge rounding, caustic etch, another cleaning, followed by a multi-step, chemical and mechanical, polishing, followed by a final cleaning step. The polished surfaces thus produced are very prone to damage by handling or otherwise.